1. Field of the Invention
The present invention relates to theatre lighting, and more particularly to controlling the temperature of lighting devices such as multiparameter lights that include electrical, optical and electromechanical components, using orientation and/or parameter information.
2. Description of Related Art
Theatre lighting devices are useful for many dramatic and entertainment purposes such as, for example, Broadway shows, television programs, rock concerts, restaurants, nightclubs, theme parks, the architectural lighting of restaurants and buildings, and other events. A multiparameter light is a theatre lighting device that includes a light source and one or more effects known as “parameters” that are controllable typically from a remotely located console. For example, U.S. Pat. No. 4,392,187 issued Jul. 5, 1983 to Bohnhorst and entitled “Computer controlled lighting system having automatically variable position, color, intensity and beam divergence” describes multiparameter lights and a central control system, or central controller. Modem multiparameter lights typically offer many different parameters, including orientation parameters such as pan and tilt, and light makeup parameters that affect the makeup of the light exiting the multiparameter light such as, for example, color, pattern, dimming, iris, focus and zoom.
A multiparameter light typically employs a light source such as a high intensity lamp as well as motors and other motion components which provide the automation to the parameters. These components are typically mounted inside of a lamp housing and generate large amounts of heat inside of the lamp housing, so that cooling by convection or forced air is required. The high intensity lamp generates the greatest amount of heat, and lamps provided by different manufactures may have differences in lumens per watt, or may have a spectral distributions that create more energy in the infrared spectrum thus further raising the internal temperature of the multiparameter light. However, motors used to automate the parameters also generate significant amounts of heat. Heat generation by the motors is a function of the number of motors within a lamp housing as well as the usage of the motors. Heat generation increases with increasing numbers of motors and with repetitive use in a high duty cycle. For example, motors within the lamp housing when used repetitively for shows or events that often repeat the change of a parameter may raise the temperature inside of the lamp housing and its components by 5 to 15 degrees Celsius. Various optical components such as lenses, filters, projection patterns, shutters, and an iris diaphragm are used along the light path, which is the path that a light beam from the lamp normally travels within the lamp housing before it is projected from the multiparameter light, to collimate the light and create and focus patterns to be projected. These optical components are selectively moved in and out of the light beam or are controllably varied when in the light beam to vary the attributes of the projected light, and generate varying amounts of heat as they interact with the light beam by reflection or absorption. For example, light collimated, condensed or filtered by the optical components may be reflected back into the lamp housing, the components of the lamp housing, or the lamp itself, causing a rise in temperature of the multiparameter light generally or in particular components thereof. Light may also be absorbed by the optical components when placed in the path of the light beam. As these components absorb the condensed or collimated light, they become heated themselves and can raise the temperature within the lamp housing.
The ambient air temperature to which the instrument is exposed may also raise the internal temperature of the lamp housing from 25 to 40 Celsius. The position of the multiparameter lamp housing also is a factor in the operating temperature, since the position may allow heat to rise in certain areas of the lamp housing. Specific examples of how the position of a multiparameter light and of how optical components in the lamp housing which lie in the path of the light beam to vary the parameters can generate different amounts of heat are shown in FIGS. 1 through 6. FIG. 1 and FIG. 2 show a filter wheel 1 of the type commonly used in multiparameter lights to set various parameters such as, for example, color and pattern; see, e.g., FIGS. 7-10 (elements 48, 49 and 51) for examples of filter wheels inside of multiparameter lights. Filter wheels are also known as color wheels. The filter wheel 1 illustratively contains eight filter positions 2-8, which are selectively rotated into the light beam to create the desired lighting effect. One of the filter positions, here position 2, is blank so that light may pass freely through the filter wheel 1. Various types of filters are suitable for use in the other filter positions 3-8, including reflecting filters such as optical thin film filters, or dichroic filters, which transmit the desired frequency of light and reflect all other frequencies, and absorbing filters such as some dyed glass filters, which transmit the desired frequency of light and absorb other frequencies. The filter wheel 1 (see FIG. 2) is rotated by a motor 10 through a shaft 9.
FIG. 3 is a schematic drawing of a section of a multiparameter light that includes a lamp 17, reflector 16, condensing lens 18, the filter wheel 1, and a focusing lens 14 within a lamp housing 11; see, e.g., FIGS. 7-10 (elements 45, 46 and 47) for examples of a reflector, lamp, and lens combination as used in various types of multiparameter lights. An arrow 12 shows the direction of forced cooling air that flows through the lamp housing (not shown) of the multiparameter light of FIG. 3, and an arrow 13 shows the natural convection current direction, or the direction of rising heat absent forced air conditions, through the lamp housing 11 of the multiparameter light of FIG. 3. The arrows 12 and 13 are parallel, indicating that the lamp housing 11 of FIG. 3 is in a horizontal position. The lamp 17, the reflector 16, and the lens 18 give off significant amounts of absorbed heat as represented by the wavy lines emanating therefrom. However, the heat emanating from the lamp 17, the reflector 16, and the lens 18 is parallel to both the forced air direction 12 and the convection current direction 13 and is effectively removed from the multiparameter light. Light from the lens 18, represented by rays 19 and 20, is unfiltered as it passes through an opening 2 in the filter wheel 1. The configuration of FIG. 3 can be thought of as a reference configuration because it results in low overall heating of the multiparameter light lamp housing.
FIG. 4 is a schematic drawing of the same section of the multiparameter light as shown in FIG. 3, but shows a reflecting filter 3 in the light beam rather than the opening 2 (FIG. 3). The arrow 12 showing the direction of forced cooling air and the arrow 13 showing the natural convection current direction are parallel, indicating that the lamp housing 11 of FIG. 4 is in a horizontal position. Light from the lens 18 is filtered as it passes through the reflecting filter 3 in the filter wheel 1, resulting in a light beam having the desired properties as represented by rays 24 and 26, and reflected light as represented by rays 23 and 25. The reflected light 23 and 25 passes back into the multiparameter light lamp housing, disproportionately increasing the temperatures of some of the internal components such as the lens 18, lamp 17, and reflector 16 relative to their temperatures in a reference operating configuration such as that of FIG. 3. Although heat from the lens 18, lamp 17, and reflector 16, which is represented by the wavy lines emanating therefrom, is parallel to both the forced air direction 12 and the convection current direction 13, more heat is generated inside the lamp housing in the configuration of FIG. 4 than in the configuration of FIG. 3 because of the reflected light. The configuration of FIG. 4 therefore results in somewhat increased heating of the lens 18, lamp 17, and reflector 16, as well as an increase of temperature in the lamp housing.
FIG. 5 is a schematic drawing of the same section of the multiparameter light as shown in FIG. 4, but shows that light from the lens 18, which is represented by rays 24 and 26, is directed in a downward direction rather than a horizontal direction (FIG. 4). The reflected light 23 and 25 passes back into the multiparameter light lamp housing, disproportionately increasing the temperatures of some of the internal components such as the lens 18, lamp 17, and reflector 16 relative to their temperatures in a reference operating configuration such as that of FIG. 3. An arrow 27 shows the direction of forced cooling air, which is traverse to the natural convection current direction as shown by the arrow 13. The convection currents can be as much as 90 degrees relative to the fan cooling currents. The wavy lines emanating from the lens 18, the lamp 17, and the reflector 16 indicate that the convection currents are not entirely dominated by the forced cooling air and cause a disproportionate increase in the temperature of the lens 18 and especially the lamp 17 and the reflector 16 when the light is directed in a downward direction. Moreover, any cooling air currents that might come from the volume of the lamp housing 11 near the lens 14 are blocked by the filter 3. The configuration of FIG. 5 results in greatly increased heating of the lens 18, lamp 17, and reflector 16, as well as an increase of temperature in the lamp housing.
FIG. 6 is a schematic drawing of the same section of the multiparameter light as shown in FIG. 3, but shows an absorbing-type color filter 4 in the light beam rather than the opening 2 (FIG. 3). The arrow 12 showing the direction of forced cooling air and the arrow 13 showing the natural convection current direction are parallel, indicating that the lamp housing 11 of FIG. 6 is in a horizontal position. Light from the lamp 17 and lens 18, which is represented by rays 34 and 38, contains undesirable frequencies which are absorbed by the filter 4, and the desired filtered light, represented by rays 35 and 39, passes freely. The amount of heat from the lens 18, lamp 17, and reflector 16, which is represented by the wavy lines emanating therefrom, is similar to that generated by the configuration of FIG. 3, and is parallel to both the forced air direction 12 and the convection current direction 13 so that it is effectively removed. However, a relatively large amount of heat is generated in the absorbing filter 4, as indicated by the wavy lines emanating therefrom, which could damage the absorbing filter 4 and could also generally raise the temperature inside the lamp housing 11. The configuration of FIG. 6 therefore potentially results in significant heating of the filter 4 and a somewhat increased general heating of some of the other components within the lamp housing 11.
Because of the presence of such substantial amounts of heat, some multiparameter lights are constructed of various high temperature materials. For example, the insulation of the wiring to the lamp may be silicon or Teflon. The lamp housing of the multiparameter light may be constructed of a high temperature polymer, which additionally helps to reduce the weight of the light and is often molded into a pleasing design shape. However, as the heat capacity of even these materials is not infinite, various cooling techniques are used. The most common cooling techniques are convection and forced air cooling. An example of a convection cooled multiparameter light is the model Studio Color® 575 wash fixture, available from High End Systems, Inc. of Austin, Tex., URL www.highend.com. In this type of multiparameter light, the convection cooled lamp housing contains the lamp, motors, optics and mechanical components, and is rotatably attached to a yoke that facilitates pan and tilt. The yoke is rotatably attached to a base, which contains the power supplies and control and communications electronics. The Studio Color 575 wash fixture and some other such products also have the capability of reducing power to the lamp when the shutter is closed for the purpose of extending lamp life. See also U.S. Pat. No. 5,515,254, issued May 7, 1996 to Smith et al. and entitled “Automated color mixing wash luminaire,” and U.S. Pat. No. 5,367,444, issued Nov. 22, 1994 to Bohnhorst et al. and entitled “Thermal management techniques for lighting instruments.” An example of a forced air cooled multiparameter light is the model Cyberlight® automated luminaire, available from High End Systems, Inc. of Austin, Tex., URL www.highend.com. In this type of multiparameter light, the forced-air cooled lamp housing is stationary and contains all of the necessary operating components, including a positionable reflector to achieve the pan and tilt parameters.
Neither convection cooling nor forced air cooling is entirely satisfactory. Convection cooling is quiet but does not dissipate as much heat as forced air cooling. Forced air cooling typically is achieved with fans which increase the operating noise of the multiparameter light.
A technique found both in forced air cooled multiparameter lights and convection cooled multiparameter lights for dealing with excessive heat in the lamp housing involves the use of a thermal switch to turn off the lamp when the temperature inside of the lamp housing exceeds specification, and then to turn on the lamp when the inside of the lamp housing falls back to a cooler temperature. FIG. 7 is a block diagram of a forced air cooled multiparameter light which has a lamp housing 40. The lamp housing 40 contains various optical components such as a reflector 45, a lamp 46, a condensing lens 47, a shutter 43 (useful for dimming), three filter wheels 48, 49 and 51, an iris diaphragm 50 (motor omitted for clarity), and a focusing lens 52 (motor omitted for clarity). The lamp housing 40 also contains a thermal switch 59, a lamp power supply 44, and a power supply 53 to power the various motors and electronics of the multiparameter light. The electronics 41 within the lamp housing 40 include a communications node for receiving communication signals and commands from a remote console (not shown) to vary the parameters of the multiparameter light, and a microprocessor for operating the various electrical and electromechanical systems of motors and other actuators (not shown for clarity), optical components, motion components, and other components of the multiparameter light, as well as for turning on and off a fan 42 in accordance with the commands. For cooling purposes, air enters the interior of the lamp housing 40 through a intake vent 54, and is drawn through the lamp housing 40 by the fan 42, and exits the lamp housing 40 through the fan 42. The thermal switch 59 is located next to the ventilation exit near the fan 42, and responds to the temperature at that point inside of the lamp housing 40 by opening the line power circuit if the temperature exceeds specification and closing the line power circuit when the temperature falls back into specification. If pan and tilt parameters are desired, a positionable reflector system (not shown) is provided after the focusing lens 52 and typically outside of the housing 40, although the reflector system may be located inside of the housing 40 if desired.
FIG. 8 is a block diagram of a convection cooled multiparameter light which has a lamp housing 55. The lamp housing 55 contains many of the same type of components as the multiparameter light of FIG. 1 (the component values may of course be different). The electronics 56 within the lamp housing 55 include a communications node for receiving communication signals and commands from a remote console (not shown) to vary the parameters of the multiparameter light, and a microprocessor for operating the electromechanical system of motors (not shown for clarity) of the multiparameter light. Air enters the interior of the lamp housing 55 through an intake vent 58 which has cooling fins, and is drawn through the lamp housing 55 by convection currents and exits the lamp housing 55 through an exhaust vent 57 which also has cooling fins. The various cooling fins may be connected to various components in the lamp housing 55 to help dissipate heat from those components. The thermal switch 59 is located next to the ventilation exit near the exhaust vent 57, and responds to the temperature at that point inside of the lamp housing 55 by opening the line power circuit if the temperature exceeds specification and closing the line power circuit when the temperature falls back into specification.
Another technique found in forced air cooled multiparameter lights for reducing the heat generated by the lamp involves the use of a variable speed fan which runs at high speed to provide a great deal of heat dissipation when required but otherwise runs at lower speeds to achieve adequate cooling with reduced fan noise. FIG. 9 is a block diagram of a forced air cooled multiparameter light which has a lamp housing 60. The lamp housing 60 contains many of the same type of components as the multiparameter light of FIG. 7 (the component values may of course be different), except that a thermal switch is not necessarily present in the line voltage circuit. Instead, a thermal sensor 66 monitors the temperature at a point inside of the lamp housing 60 and furnishes the measurements to a sensor interface 65. The sensor interface 65 is part of the electronics within the lamp housing 60, which also include a communications interface 61 for receiving communication signals and commands from a remote console (not shown) to vary the parameters of the multiparameter light, and a microprocessor 62 for operating the electromechanical system of motors (not shown for clarity) of the multiparameter light through a motor control interface 64 and for operating the speed of a variable speed fan 67 through a fan control interface 63. Air enters the interior of the lamp housing 60 through an intake vent 68, and is drawn through the lamp housing 60 by the variable speed fan 67 and exits the lamp housing 60 through the variable speed fan 67. The microprocessor 62 monitors the temperature within the lamp housing 60 and adjusts the speed of the fan 67 to maintain the temperature within the lamp housing 60 within specification. Fan speed may be set by the microprocessor 62 in various ways, such as, for example, by consulting a temperature-to-fan speed ratio table stored in local memory (not shown) to which the microprocessor 62 has access in a manner well known in the art.
If desired, a thermal switch such as the switch 59 (FIG. 7) may be added to the multiparameter light of FIG. 9 to provide protection against overheating when the fan 67 is operating at full speed.
FIG. 10 is a block diagram of a forced air cooled multiparameter light that has the same type of components as the multiparameter light of FIG. 7, but has separate base and lamp housing sections with respective housings 70 and 71. The base housing 70 contains the communications interface 61, the microprocessor 62, the fan control interface 63, the motor control interface 64, the thermal sensor interface 65, the lamp power supply 44, and the motor and electronics power supply 53. The lamp housing 71 contains the thermal sensor 66, the reflector 45, the lamp 46, the condensing lens 47, the shutter 43, the filter wheels 48, 49 and 51, the iris diaphragm 50, and the focusing lens 52. Various wires are run between the base housing 70 and the lamp housing 71 (some wires are omitted for clarity) through a wireway 73, which typically is a flexible conduit or a pathway between the bearings used to attach the lamp housing 71 to the base housing 70 on pan and tilt lights. Air enters the interior of the lamp housing 71 through an intake vent 74, and is drawn through the lamp housing 71 by the variable speed fan 72 and exits the lamp housing 71 through the variable speed fan 72. The microprocessor 62 monitors the temperature within the lamp housing 71 and adjusts the speed of the fan 72 to maintain the temperature inside of the lamp housing 71 within specification.
In the multiparameter lights of FIGS. 9 and 10, an electronic circuit controls the fan speed in accordance with signals from a thermal sensor. As the temperature inside of the lamp housing rises, the sensor provides a signal to the electronic circuit that in turn increases the speed of the fan. This increased fan speed provides greater airflow and in turn lowers the temperature of the lamp housing and the components contained therein. While effective for temperature control, this solution is disadvantageous in settings where the ambient temperature is high and a high noise level is not acceptable. Such settings are quite common. For example, multiparameter lights are often operated in groups in, for example, churches, theatres and television studios, where the ambient temperature in the vicinity of a group of lights may rise to above about 50 degrees Celsius. When the ambient temperature is high, the variable speed fan of a multiparameter light operates near or at maximum speed and creates noise. Since several fans operating in close proximity at maximum speed create quite a lot of noise, forced air cooled multiparameter lights are not entirely suitable for use at locations where a high noise level is not acceptable. Convection cooled multiparameter lights may be used where the noise of a forced air cooled multiparameter light is unacceptable. However, convection cooled multiparameter lights typically utilize lamps that generate less heat and are constructed of expensive high temperature materials.
For either convection cooled or forced air cooled multiparameter lights, a thermal sensor or thermal cutoff switch may be employed to remove the supply voltage to the lamp if the temperature monitored by the sensor reaches a maximum allowable safe temperature. Unfortunately, this means that if the multiparameter light is operated in high enough ambient temperatures, the lamp may shut down. It is possible that during a performance event with high ambient temperatures, one or more of the multiparameter lights in the event may inadvertently shut down, causing great inconvenience and distraction.
Permitting a multiparameter light to run too hot is not a good option. As the temperature of the lamp housing increases, the temperature of all the components in the lamp housing also increases. Typically, lamp life is shortened. The motors used for the automation can easily reach critical operating temperatures and sustain damage. Electronic circuitry if contained within the lamp housing, may reach operating temperatures that greatly shorten the life of components therein such as semiconductors, capacitors and transformers. Additional components and materials used for the construction and proper operation of the instrument and lamp housing may also be affected, such as polymers, elastomers and lubricants.